Higher floral richness promotes rarer bee communities across remnant and reconstructed tallgrass prairies, though remnants contain higher abundances of a threatened bumble bee (Bombus Latreille)

Managing and restoring tallgrass prairie ecosystem is an important form of pollinator conservation in the Midwestern United States. Prairie reconstruction has been found to enhance native bee diversity and abundance, but it is less clear if prairie reconstruction conserves species thought to be at-risk. We reanalyze a previously published dataset on the bee communities of reconstructed and remnant prairie in the US state of Minnesota to investigate how the abundance of at-risk species respond to local factors, such as floral diversity and prairie type (reconstructed or remnant), and landscape factors, in the form of surrounding agricultural production. We defined at-risk species in two ways. For bumble bees, we used the IUCN red list of bumble bees for North America. As other species in the bee community have not been systematically evaluated, we used an independent data set to calculate a community-level measure of rarity as a proxy for species risk. We calculated community rarity metrics using a Species Weighted Mean (SWM) approach, with species level rarity (relative abundance and site occurrence) derived from a regional dataset comprised of over 30,000 specimens from across the US state of Minnesota. We found that the declining bumble bee Bombus fervidus had higher abundances in remnant rather than reconstructed prairies. Floral richness was associated with rarer bee communities (lower SWM values) across remnant and reconstructed prairies. We show that planting and managing prairies for floral diversity promotes bee communities with rarer species, but that remnants better support some at-risk species such as Bombus fervidus.